I agree with your post. Like others, I have cross-eye dominance and shoot with my non-dominant hand for accuracy. It's surprisingly not as awkward as many might think, but I must admit, I think I would use my dominant hand if I was putting the gun to my own head. That said, there's no way for me to determine what BL was thinking during those final moments.
It is one of the reasons I keep wondering if he was doing something else with his right hand. He had a notebook and "half-note" (whatever that might mean) inside his dry bag. Had he written everything he was going to write before he left home? Because what isn't mentioned in the autopsy report is a pen, pencil, or any other tool for writing. It could have simply been lost, because he didn't put it back in the dry bag with the other items, or he maybe never had a writing tool to begin with. But mixing the lack of pen with the "half-note" comment still makes me wonder if there was a second half of the note, which he was writing on with his right hand, and the pen and paper got washed away with the rain and rising water. IDK...
We don't know anything about what was written in that notebook other than that the FBI said he claimed responsibility for GP's death. If he had only a few very personal items along, claimed responsibility, wrote a suicide note, had a gunshot wound to the head, and recoil evidence to the left hand bones, maybe there just isn't any reason to question it as a suicide.
But if the ME and forensic anthropologist were wrong and there was reason to think his death was by murder, I would want to see his killer prosecuted, for all the reasons you stated. I just don't think anyone else was in that swamp with BL when the trigger was pulled...jmo.
Good point about the lack of a writing instrument.
He could have been holding something in his right hand as you suggest. Or it's possible he had injured his right hand somehow while in the swamp so he would have used his left to shoot IF he was already comfortable doing that. I admit I'm not really up on autopsy stuff and I know they can tell alot (especially since a forensic anthropologist was involved.) But unless he had broken bones in his right hand, I don't know that a premorbid injury to the "flesh" of that hand would have left signs by the time the skeletal remains were found. I'm also not sure there would have been recoil evidence on his shooting hand by then. But I could be wrong-- JMO.